I can't answer the question fully, obviously. I can merely reiterate my memories of the time.
- There was a lot of unhappiness with the monk in 1E. The class was considered unpowered and unplayable. They wanted to fix that, tried to in Dragon Magazine, and finally moved the monk to Oriental Adventures instead.
- There was great unhappiness with the assassin. They believed it tarnished the game's imagine, I think. They got rid of that class, declaring that any class with a reprehensible mindset like that could be an assassin (a legitimate point, I suppose.)
- There was great uproar over the bard:
In 1E, you did not start playing a bard, as a bard, but as a fighter. At 7th level, you changed to thief (rogue.) At 7th level as a thief, you changed to bard. So, at 1st level, the bard had the abilities and hit points of a 7th level fighter, a 7th level thief, a 1st level druid of sorts, and bardic abilities also. This was considered overpowered and unwieldly to play (going through 14 levels before you got to the bard part!) and so they wanted to fix it. People liked bards, and they wanted to keep the concept; they just wanted to make it more workable.
- Psionics in 1E were rather unwieldly, or so thought many people. 10 psionic combat rounds occurred during the standard 1 minute round, so everyone had to stop what they were doing while the psionic turn was played out. There were many other complaints about psionics as well. They kept the concept, some people wanted to preserve it, and they created the Psionicist class in 2E.
- The cavalier of 1st edition, and especially the cavalier-paladin of 1st edition, were a bit overwhelming as classes, or so thought many. (See the 1E Unearthed Arcana.) They wanted to keep the classes, but change them a bit.
- I remember that people wanted a lot of modification of the ranger.
- Everyone thought (including me) that the cleric had too few spells, and was underpowered (until he got Heal/Harm, and then he was overpowered because of that one spell.) They wanted to improve the cleric, expound on him, expand the class. And they did.
- The druid's spell lists and cleric's spell lists were combined. The druid thus got a vastly greatly choice of spells (which she needed) while keeping her powers. A lot of people thought the druid was useless in a dungeon (I tended to agree with them.)
- The idea that magical armor was weightless was abandoned. Instead, it simply caused no 'encumbrance' while still weighing normally. I don't know why the change, but there it is.
- In 1E, ANYONE who donned elven chain could cast arcane spells in it, but in 2E, only elves in elven chain could cast arcane spells in it (greatly to the disappointment of many eager wizards and bards ... elven chain was as popular as hotcakes in 1E.)
- The superpowerful Shapechange spell, 9th level wizard, was nerfed. Why do I say superpowerful? Because it allowed you to become ANYTHING short of a demigod or singular creature, and gain ALL it's powers except those solely based on the mind like memorized spells, and magic resistance.
In short, want to be a tarrasque? Be a tarrasque! And then it takes two Wishes to kill you too, and then only if you are reduced to -20 hit points first! Assuming there are two or more tarrasques in your campaign world, of course. (Heck, theoretically, you could become a Solar with the original spell, and if that doesn't take the cake, what does?)
- The illusionist was drastically modified, after many complaints. Spells went up to 7th level in 1E, expanded to 9th level in 2E. Illusionists gained access to regular wizard spells (and wizards, gained access to illusionist spells.) Illusionists became a more viable class. And all the spellcasting races could become illusionists, not just gnomes.
- Illusion spells were better quantified as to their limits. In 1E, you could - theoretically - create 20 20th level warriors with a spectral force (it was in Dragon Magazine.) They put limits on the chain of spells that involved such illusions in 2E, while still leaving them as extremely potent spells that lended themselves to creativity - Phantasmal Force, Improved Phantasmal Force, Spectral Force, Advanced Illusion, Permanent Illusion, Programmed Illusion.
They better specified when saving throws were allowed for such spells, and when saving throws were *not* allowed for such spells.
- Magic Resistance was massively modified. In 1E, it was based on 11th level - if the opponent was higher than 11th, your resistance went down, and if below 11th, it went up. Basically, if your opponent was an archmage (18th level or higher) your magic resistance was useless. Autokill coming in? Say your prayers!
In 2E, they changed magic resistance. 75% was 75%, regardless of level or other considerations (which led to a whole number of spells being created to get around this problem ... and in 3E, they went back to a more 1E approach to magic resistance, now called spell resistance.)
- They played down artifacts and relics in 2nd edition. They were there, but there were fewer of them, and DMs were discouraged from their use (or, as they said, artifacts were the McGuffins, things that made the plot go, and not much use otherwise except as gamebreakers.)
- They stressed the problems and pitfalls of playing evil alignments, and discouraged this amongst Player Characters.
In 1E, there was little bias one way or another, but in 2E the stress was on good alignment, as good alignment (hopefully) led to party cooperation and unity, and thus to more fun for the players (and DM.)
They even displayed examples of how evil alignment, if played properly, would ruin the fun by default.
- They tried to address the reality that they had thousands of monster types out there, and couldn't cram them all into one book, so what to do? (They even asked this question in Dragon Magazine: What to do? Send us your suggestions.)
They came up with the idea of the giant 3 ringed folders. You bought monster supplements, and put them in there page by page, amongst your other monsters (if you bought all of the supplements, you now had this giant hefty book that would rival a 2 litre bottle of pop for weight, but hey ... they sure had a lot of monsters, with some neat drawings, and lots and lots of descriptions.)
- They created a kind of Habitrail Situation. Don't know what I'm talking about?
You know the cage in which hampsters and gerbils run on the wheel? Well, the company Habitrail came out with these, and supplemental packages, of tubes and corridors and other chambers, until you had a whole city of tubes and chambers and places for the gerbil or hamster to go.
2nd Edition was sorta like that. Whereas 1st Edition was a closed system of sorts (the PHB, MM, DMG, and Unearthed Arcana, and maybe 2 or 3 other books), you could keep adding books, supplements, boxed sets, stuff from Dragon and other magazines, and stuff from 3rd party supplements to your game, again and again, book upon book, magazine upon magazine, until you had hundreds of sources, with 2nd Edition.
- The Habitrail Situation led to the rapid expansion of the wizard's spell list. Many books, supplements, boxed sets, Dragon Magazines, and other products, came out with new spells for the wizard. There was a deluge of such spells, until thousands of spells existed (and amongst them, many variants of individual popular spells.)
In 1st edition, you had a limited spell list for the wizard. Another even more limited list for the illusionist. Limited lists for the unique 1st edition classes from Dragon Magazine (such as the witch, death master, hedge wizard, and even ... zee chef.) Arcane classes were heavily defined by what spells they could cast, and at what level (for example, the Red Wizards of Thay specialized in invocation/evocation could throw Fireball as a 2nd level spell!!)
In 2nd Edition, all the lists became standardized into one grand list, The Grand List as it were, of these countless hundreds, even thousands, of spells.
- Everyone was complaining about Level Limits. They were quite restrictive, if you compare them with what 3rd Edition characters can do.
For example, elves were basically limited to 5th level as fighters, 9th level as wizards, and they could not be clerics, druids, paladins, rangers (you heard that right), illusionists, or monks. If they had extremely high stats, they could advance up to 2 levels higher than the standard limits.
These limits were raised and some new classes allowed before 2nd Edition came out, but in 2ND EDITION the level limits were raised greatly. Elves, for example, could now go to 14th level as wizards, and with Slow Advancement, attain higher levels yet.
(Dwarves still could not cast Arcane Spells ... but they could be clerics now, and made very fine ones. Dwarves had to wait until 3E to become wizards ... but then, *kender* could - theoretically - become wizards in 3E, too. Not that they did, mind you ...)
So, there were some of the changes. I guess these were Design Goals, and the changes were made to suit these Design Goals, and to make a lot of players happier (they had been sending in correspondence to Dragon via snail-mail for countless years) and so we had 2nd Edition AD&D.
Just some commentary and sharing of memories here.
Yours Sincerely
Edena_of_Neith